Workpiece grinding method

ABSTRACT

A method of grinding a back side of a workpiece having a device region and a peripheral surplus region on a front side thereof includes covering the front side of the workpiece with a protective member, holding a protective member side of the workpiece by a holding surface of a chuck table that is rotated around a rotational axis inclined at an angle of 45 to 180 degrees relative to a vertical direction, and grinding the back side of the workpiece corresponding to the device region by a grindstone rotated around a rotational axis orthogonal to the holding surface while supplying grinding water, to form a circular recess and an annular reinforcement section surrounding the circular recess. When grinding, discharge of the grinding water containing abrasive grains dropped from the grindstone is promoted by the inclination of the workpiece.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a method of grinding a plate-shapedworkpiece such as a semiconductor wafer by a grindstone.

Description of the Related Art

A workpiece in which a plurality of devices such as integrated circuits(ICs) and large scale integrations (LSIs) formed on a front side thereofhas its back side ground to be thinned to a predetermined thickness, andis further divided by a dividing apparatus such as a dicing apparatusinto individual device chips, which are used for various electronicapparatuses.

A grinding apparatus for grinding the back side of the workpieceincludes a chuck table adapted to hold the workpiece to which a frontside protective member formed of a resin or the like is adhered, agrinding unit in which a grindstone for grinding the workpiece held bythe chuck table is rotatably supported, and grinding water supplyingmeans supplying grinding water to the grindstone through a flow passageformed along an axis of a spindle constituting the grinding unit. By thegrinding apparatus configured in this way, the workpiece can be groundefficiently.

In recent years, for achieving reductions in the weight and size ofdevice chips, it has been demanded in the wafer grinding method to makethe workpiece smaller in thickness. The wafers thus made thinner,however, are lowered in rigidity, to become difficult to handle, and maybe damaged or broken during when being carried or in other similarsituations. In view of this problem, there is a grinding method whereinthe workpiece is ground and thinned to, for example, 100 μm or below,then, only that region of the back side of the workpiece whichcorresponds to the device region on the front side is further ground andthinned, to leave on the back side an annular reinforcement sectioncorresponding to the peripheral surplus region surrounding the deviceregion on the front side, thereby ensuring easy handling of the thinnedworkpiece (see, for example, Japanese Patent Laid-Open No. 2007-19461).

SUMMARY OF THE INVENTION

In the grinding method as above, however, since the annularreinforcement section is formed on the back side of the workpiece, theannular reinforcement section would serve as a bank during grinding, sothat grinding water containing abrasive grains dropped from thegrindstone would stagnate in the circular recess of the workpiece. Then,the dropped abrasive grains stagnating in the circular recess of theworkpiece are dragged in by the grindstone during grinding, and adhereto the grinding surface at the tip of the grindstone. When grinding bythe grindstone with the dropped abrasive grains adhering to the grindingsurface at the tip of the grindstone is continued, scratches may beformed on the ground surface of the workpiece or cracking of theworkpiece may be generated.

It is therefore an object of the present invention to provide aworkpiece grinding method which is of the type of grinding a region ofthe back side of the workpiece corresponding to a device region on thefront side, to form a circular recess, and to form an annularreinforcement section in a region of the back side of the wafercorresponding to a peripheral surplus region surrounding the deviceregion, and by which formation of scratches on the back side of theworkpiece, generation of cracks in the workpiece, and the like troublescan be prevented.

In accordance with an aspect of the present invention, there is provideda workpiece grinding method of grinding by a grindstone a back side of aworkpiece having on a front side thereof a device region in which aplurality of devices are formed and a peripheral surplus regionsurrounding the device region. The workpiece grinding method includes afront side protecting step of covering the front side of the workpiecewith a protective member, a holding step of holding a protective memberside of the workpiece by a holding surface of a chuck table that isrotated around a rotational axis inclined at an angle of 45 to 180degrees relative to a vertical direction, after the front sideprotecting step is performed, and a grinding step of grinding the backside of the workpiece corresponding to the device region by thegrindstone rotated around a rotational axis orthogonal to the holdingsurface while supplying grinding water, to form a circular recess and anannular reinforcement section that corresponds to the peripheral surplusregion and that surrounds the circular recess. In the grinding step,discharge of the grinding water containing abrasive grains dropped fromthe grindstone is promoted by the inclination of the workpiece.

Preferably, the protective member is an adhesive tape.

Preferably, in the grinding step, the grindstone is positioned in such amanner that a rotational trajectory of the grindstone and a dischargeposition of the grinding water containing the abrasive grains droppedfrom the grindstone do not overlap each other since the dischargeposition is located at a lowermost point of the chuck table whoserotational axis is inclined.

According to the present invention, in the grinding step, the dischargeof the grinding water containing the abrasive grains dropped from thegrindstone is promoted by the inclination of the workpiece. Therefore,the grindstone is restrained from dragging in the dropped abrasivegrains during grinding, so that formation of scratches on the back sideof the workpiece, generation of cracks in the workpiece, and the liketroubles can be prevented from occurring.

In the grinding step, the discharge position of the grinding watercontaining the abrasive grains dropped from the grindstone is located atthe lowermost point of the chuck table whose rotational axis isinclined. Therefore, where the grindstone is positioned in such a mannerthat the rotational trajectory of the grindstone and the dischargeposition of the grinding water do not overlap each other, the dischargeof the grinding water containing the abrasive grains dropped from thegrindstone is thereby performed more efficiently.

The above and other objects, features and advantages of the presentinvention and the manner of realizing them will become more apparent,and the invention itself will best be understood from a study of thefollowing description and appended claims with reference to the attacheddrawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view depicting an example of a workpiece and aprotective member for protecting a front side of the workpiece;

FIG. 2 is a sectional view depicting a state in which the workpiece heldby a chuck table is ground by a grindstone;

FIG. 3 is a schematic perspective view for explaining a state in which arotational trajectory of the grindstone and a discharge position ofgrinding water do not overlap each other; and

FIG. 4 is a sectional view depicting a state in which the grinding wateris discharged from a position on the back side of the workpiece ground.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A workpiece W depicted in FIG. 1 is, for example, a semiconductor waferwhich is circular plate-like in external form, the base material ofwhich is silicon, and which is provided on a front side Wa thereof witha device region Wa1 and a peripheral surplus region Wa2 surrounding thedevice region Wa1. The peripheral surplus region Wa2 is that region ofthe front side Wa of the workpiece W which is on the outside of animaginary line L1 represented by an alternate long and two short dashesline in FIG. 1. The device region Wa1 is partitioned in a grid patternby a plurality of division lines (streets) S intersecting orthogonally,and a device D such as an IC is formed individually in each of regionspartitioned in the grid pattern. A back side Wb of the workpiece W is ato-be-ground surface to be subjected to grinding. Note that theworkpiece W may be formed from gallium arsenide, sapphire, galliumnitride, silicon carbide or the like, other than silicon.

Each of steps in the case of carrying out a grinding method according tothe present invention to grind the workpiece W depicted in FIG. 1 to apredetermined thickness will be described.

(1) Front Side Protecting Step

In subjecting the workpiece W to grinding, for example, a circularprotective member T1 substantially the same in diameter as the workpieceW is adhered to the front side Wa of the workpiece W, resulting in astate in which the device region Wa1 and the peripheral surplus regionWa2 are covered and protected by the protective member T1. Theprotective member T1 may be, for example, an adhesive tape including abase material layer and an adhesive layer, but it not limited thereto. Ahard plate having rigidity such as a glass substrate may be adhered tothe front side Wa with an adhesive, to serve as the protective member,or a liquid resin may be applied to the front side Wa and the resin maybe cured by heating, irradiation with ultraviolet rays, or the like, toform a protective member covering the front side Wa of the workpiece W.

(2) Holding Step

The workpiece W with its front side Wa covered with the protectivemember T1 is carried to a grinding apparatus 2 depicted in FIG. 2. Thegrinding apparatus 2 includes a chuck table 3 adapted to hold theworkpiece W by suction, and a grinding unit 4 adapted to grind theworkpiece W by grindstones 42 b. The chuck table 3 includes, forexample, a holding section 30 which is circular plate-like in externalform, is formed from a porous member or the like and is adapted to holdthe workpiece W by suction, and a frame body 31 supporting the holdingsection 30. The holding section 30 is communicating with a suctionsource (not depicted) composed of a vacuum generating apparatus, acompressor or the like through a piping, a rotary joint or the like. Asuction force generated by a suction operation of the suction source(not depicted) is transmitted to the holding surface 30 a, whereby thechuck table 3 holds the workpiece W on the holding surface 30 a bysuction.

The chuck table 3 can be reciprocated in a Y-axis direction by Y-axisdirection feeding means (not depicted). In addition, one end of a rotaryshaft 33 is connected to a bottom surface side of the chuck table 3, anda motor 34 is connected to the other end of the rotary shaft 33. Therotary shaft 33 is inclined at an angle of 45 to 180 degrees relative tothe vertical direction (Z-axis direction), and the chuck table 3 is alsoinclined relative to the vertical direction at the same angle as theinclination angle of the rotary shaft 33. With the motor 34 rotating therotary shaft 33, the chuck table 3 is also rotated around an axis of therotary shaft 33 which is inclined at the predetermined angle.

The grinding unit 4 includes a rotary shaft 40, a motor (not depicted)for rotationally driving the rotary shaft 40, a circular mount 41connected to a lower end of the rotary shaft 40, and a grinding wheel 42detachably connected to a lower surface of the mount 41. The grindingwheel 42 includes a wheel base 42 a, and a plurality of grindstones 42 bhaving a substantially rectangular parallelepiped shape and arranged inan annular pattern at a peripheral portion of a bottom surface of thewheel base 42 a. The grindstones 42 b are formed, for example, bybinding diamond abrasive grains or the like with a resin bond, a metalbond or the like. The grindstones 42 b arranged in an annular patternare so arranged that, for example, the diameter of an outermostcircumference thereof is larger than the radius of the device region Wa1of the workpiece W and is smaller than the diameter of the device regionWa1, and that the diameter of an innermost circumference thereof issmaller than the radius of the device region Wa1.

In addition, the rotary shaft 40 is inclined at an angle of 45 to 180degrees relative to the vertical direction (Z-axis direction), like therotary shaft 33 of the chuck table 3, and the grinding unit 4 as a wholeis also inclined relative to the vertical direction at the same angle asthe inclination angle of the rotary shaft 40. Specifically, for example,in the case where the rotary shaft 33 of the chuck table 3 is inclinedat 45 degrees relative to the vertical direction, the rotary shaft 40 isalso inclined at 45 degrees relative to the vertical direction, and thegrindstones 42 b grinds the back side Wb of the workpiece W whilerotating around an axis of the rotary shaft 40 which is orthogonal tothe holding surface 30 a of the chuck table 3.

The grinding unit 4 inclined at the predetermined angle relative to thevertical direction can be moved in a direction (the axial direction ofthe rotary shaft 40) for spacing away from or coming closer to theholding surface 30 a of the chuck table 3 which is inclined, by grindingfeeding means (not depicted).

The rotary shaft 40 is formed therein with a flow passage 43 serving asa passage for grinding water, in the manner of penetrating the rotaryshaft 40 in the axial direction of the rotary shaft 40. The flow passage43 passes through the mount 41, and has a lower end side opening at abottom surface of the wheel base 42 a such that the grinding water canbe jetted toward the grindstones 42 b. In addition, grinding watersupplying means 44 supplying the grinding water such as pure water intothe flow passage 43 communicates with the upper end side of the flowpassage 43.

As illustrated in FIG. 2, in the holding step, first, the workpiece Wwith the protective member T1 adhered to the front side Wa thereof ismounted on the holding surface 30 a of the chuck table 3 having therotary shaft 33 inclined, for example, at 45 degrees relative to thevertical direction, in such a manner that the center of the holdingsurface 30 a and the center of the workpiece W are substantially inregister and that the back side Wb of the workpiece W is exposed. Then,the suction force generated by the suction source (not depicted) istransmitted to the holding surface 30 a, resulting in that theprotective member T1 side of the workpiece W is suction held by theholding surface 30 a of the chuck table 3.

(3) Grinding Step

Next, the chuck table 3 with the workpiece W held thereby is moved inthe Y-axis direction to a position under the grinding unit 4 inclined atan angle of 45 degrees relative to the vertical direction, and alignmentbetween the grinding wheel 42 possessed by the grinding unit 4 and theworkpiece W is conducted. The alignment is performed, for example, insuch a way that an inner circumferential edge of the peripheral surplusregion Wa2 of the workpiece W, or an imaginary line L1 on the back sideWb, and part of an outermost circumference of a rotational trajectory ofthe grindstones 42 b overlap each other, and that the rotationaltrajectory of the grindstones 42 b passes through the rotational centerof the workpiece W. Further, in the grinding step, a discharge positionof the grinding water containing abrasive grains dropped from thegrindstones 42 b as will be described later is a lowermost point,depicted in FIGS. 2 and 3, of the chuck table 3 inclined at 45 degreesrelative to the vertical direction. Therefore, in order that therotational trajectory of the grindstones 42 b represented by a dottedline in FIG. 3 and the discharge position of the grinding water do notoverlap each other, the grindstones 42 b are positioned, for example, ata predetermined position on the −Y-direction side which is on theopposite side of the center of the workpiece W from the dischargeposition on the +Y-direction side. Note that the positioning of thegrindstones 42 b is not limited to the example in the presentembodiment. The grindstones 42 b may be positioned at a predeterminedposition for describing either one of the rotational trajectoriesrepresented by alternate long and short dash lines in FIG. 3, on theback side Wb of the workpiece W, such that the discharge position of thegrinding water containing the abrasive grains dropped and the rotationaltrajectory of the grindstones 42 b do not overlap each other.

After the alignment between the grindstones 42 b and the workpiece W isconducted, as illustrated in FIG. 2, the grindstones 42 b are rotatedattendant on rotational driving of the rotary shaft 40 by the motor (notdepicted). In addition, grinding feeding in a direction of arrow E, inwhich the grinding unit 4 is brought closer to the holding surface 30 aof the chuck table 3, is performed, whereby the grindstones 42 b inrotation are put into contact with the back side Wb of the workpiece W,and the back side Wb is ground. Besides, during grinding, the workpieceW held on the chuck table 3 is also rotated, attendant on the rotationof the chuck table 3 around an axis of the rotary shaft 33 inclined atan angle of 45 degrees relative to the vertical direction.

During the grinding, for example, the grindstones 42 b are rotated insuch a manner that the rotational center of the workpiece W is alwayslocated on the inner side of the outermost circumference of therotational trajectory of the grindstones 42 b and on the outer side ofthe inner circumference of the rotational trajectory. Further, thegrindstones 42 b are rotated in such a manner that the outermostcircumference of the rotational trajectory of the grindstones 42 b doesnot contact a peripheral region of the back side Wb corresponding to theperipheral surplus region Wa2 of the workpiece W, or does not largelyprotrude to the outer side beyond the imaginary line L1. Therefore, thegrindstone 42 b grind a central region of the back side Wb correspondingto the device region Wa1 of the workpiece W in a circular recess form,whereby a circular recess Wb1 is formed in the central region of theback side Wb corresponding to the device region Wa1, as depicted in FIG.4. In addition, an annular reinforcement section Wb2 which correspondsto the peripheral surplus region Wa2 and surrounds the circular recessWb1 is formed on the back side Wb of the workpiece W, in the manner ofprojecting in the +Z-direction.

During the grinding, the grinding water M is supplied through the flowpassage 43 in the rotary shaft 40 to the site of contact between thegrindstones 42 b and the workpiece W, to cool and wash the site ofcontact between the grindstones 42 b and the back side Wb of theworkpiece W. The washing water reaching the site of contact is caused bya centrifugal force generated due to the rotation of the chuck table 3to flow through gaps between the grindstones 42 b to the exterior,together with grinding swarf and the abrasive grains dropped from thegrindstones 42 b. Then, in the grinding method according to the presentinvention, the inclination of the workpiece W suction held on the chucktable 3 inclined at 45 degrees relative to the vertical direction causesthe grinding water M containing the abrasive grains dropped from thegrindstones 42 b to flow on the circular recess Wb1 toward the dischargeposition depicted in FIG. 4. Besides, the grinding water M isaccelerated by the inclination of the workpiece W, and flows over theannular reinforcement section Wb2 at the discharge position, to bedischarged to the outside of the workpiece W. In addition, since thedischarge position of the grinding water M and the rotational trajectoryof the grindstones 42 b do not overlap each other, discharge of thegrinding water M containing the abrasive grains dropped from thegrindstones 42 b is not obstructed. After the workpiece W is ground to adesired thickness while supplying the grinding water M, the grindingunit 4 is spaced away from the workpiece W, whereby the grinding isfinished.

As has been described above, the grinding method according to thepresent invention includes the front side protecting step of coveringthe front side Wa of the workpiece W with the protective member T1, theholding step of holding the protective member T1 side of the workpiece Wby the holding surface 30 a of the chuck table 3 that is rotated aroundthe rotational axis 33 inclined at an angle of 45 to 180 degreesrelative to the vertical direction, after the front side protecting stepis performed, and the grinding step of grinding the back side Wb of theworkpiece W corresponding to the device region Wa1 by the grindstones 42b rotated around the rotational axis 40 orthogonal to the holdingsurface 30 a while supplying the grinding water M, to form the circularrecess Wb1 and the annular reinforcement section Wb2 that corresponds tothe peripheral surplus region Wa2 and surrounds the circular recess Wb1.Therefore, in the grinding step, the discharge of the grinding water Mcontaining the abrasive grains dropped from the grindstones 42 b ispromoted by the inclination of the workpiece W. Accordingly, thegrindstones 42 b is restrained from dragging in the dropped abrasivegrains during grinding, and formation of scratches on the back side Wbof the workpiece W, generation of cracks in the workpiece W, and thelike troubles can be prevented.

In addition, in the grinding step, the discharge position of thegrinding water M containing the abrasive grains dropped from thegrindstones 42 b is located at the lowermost point of the chuck table 3whose rotational axis 33 is inclined. Therefore, where the grindstones42 b are positioned in such a manner that the rotational trajectory ofthe grindstones 42 b and the discharge position of the grinding water Mdo not overlap each other, the discharge of the grinding water Mcontaining the abrasive grains dropped from the grindstones 42 b isthereby performed more efficiently.

Note that the grinding method according to the present invention is notlimited to the above embodiment; in addition, each of the configurationsof the grinding apparatus 2 illustrated in the attached drawings is notlimitative, and appropriate modifications can be made within such arange that the effects of the invention can be produced. For instance,the supply of the grinding water to the site of contact between thegrindstones 42 b and the workpiece W may not be conducted through therotary shaft 40 of the grinding unit 4, and the grinding water may besupplied to the site of contact between the grindstones 42 b and theworkpiece W from the outside by use of a jet nozzle.

The present invention is not limited to the details of the abovedescribed preferred embodiment. The scope of the invention is defined bythe appended claims and all changes and modifications as fall within theequivalence of the scope of the claims are therefore to be embraced bythe invention.

What is claimed is:
 1. A workpiece grinding method of grinding by agrindstone a back side of a workpiece having on a front side thereof adevice region in which a plurality of devices are formed and aperipheral surplus region surrounding the device region, the workpiecegrinding method comprising: a front side protecting step of covering thefront side of the workpiece with a protective member; a holding step ofholding a protective member side of the workpiece by a holding surfaceof a chuck table that is rotated around a rotational axis inclined at anangle of 45 to 180 degrees relative to a vertical direction, after thefront side protecting step is performed; and a grinding step of grindingthe back side of the workpiece corresponding to the device region by thegrindstone rotated around a rotational axis orthogonal to the holdingsurface while supplying grinding water, to form a circular recess and anannular reinforcement section that corresponds to the peripheral surplusregion and that surrounds the circular recess, wherein in the grindingstep, discharge of the grinding water containing abrasive grains droppedfrom the grindstone is promoted by the inclination of the workpiece. 2.The workpiece grinding method according to claim 1, wherein theprotective member is an adhesive tape.
 3. The workpiece grinding methodaccording to claim 1, wherein in the grinding step, the grindstone ispositioned in such a manner that a rotational trajectory of thegrindstone and a discharge position of the grinding water containing theabrasive grains dropped from the grindstone do not overlap each othersince the discharge position is located at a lowermost point of thechuck table whose rotational axis is inclined.